The recovery of resources, such as natural gas or oil, from underground formations typically entails drilling a wellbore to the formation while circulating a drilling fluid, such as a water-based or oil-based drilling mud, within the wellbore. The drilling fluid flows down through the drill pipe (sometimes called a “drill string”), exits the pipe at a location adjacent the drill bit and then flows up through an annulus formed between the outside of the pipe and the wellbore wall. Circulation of the drilling fluid lubricates the drill bit and removes cuttings from the wellbore.
One problem encountered in such a resource recovery process is the loss of the drilling fluid to the underground formation during circulation of the fluid in the wellbore (a problem sometimes referred to as “lost circulation”). Drilling fluids may be lost to the underground formation (instead of circulating back up the wellbore) for a variety of reasons, such as, for example, the natural porosity of formation. Lost circulation can be problematic for several reasons, including, the high cost of replacing lost drilling fluids and the need to interrupt drilling until a problem resulting from lost circulation (such as breakage of the drill bit) is solved. Loss of drilling fluid into fractured, vugular or rubblized rock formations during the drilling operation of an oil or gas well may also raise safety concerns.
To address the problem of the loss of the drilling fluid, “lost circulation materials” (“LCMs”), are sometimes injected into the wellbore in an attempt to seal the pores of the porous underground formation. One commonly used lost circulation material is cement. Cement as an LCM, however, has a number of drawbacks: it is only of limited sealing effectiveness; it is prone to cracking; it requires a very long time (approximately 24 hours) to cure; it is typically of a viscosity that does not allow it to be squeezed into cracks in an underground formation; and it must remain immobile to cure.
As a result, synthetic polymers, such as polyurethanes, have also been proposed for use as a lost circulation material. As an LCM, polyurethanes have, however, also been difficult to implement. For example, many previous polyurethane-forming compositions have had an unacceptably short pot-life (i.e., the amount of time the combination of an active-hydrogen functional component, such as a polyol, and an isocyanate-functional component remains pumpable). As a result, complicated and cumbersome equipment options have been proposed to keep the reactive components separated during injection into the wellbore.
The use of blocked polyisocyanates to form polyurethane lost circulation materials has been proposed as an alternative. Blocked polyisocyanates, however, require removal of the blocking agent in order for the isocyanate groups to react with an active-hydrogen functional component. When a liquid system is contained under pressure, as is the case in an LCM application, it is difficult, if not impossible, to remove the blocking agent. In addition, blocked polyisocyanate resins are usually very high in viscosity. As a result, they can be very difficult to pump down the well bore without the use of solvents and/or plasticizers, which can be undesirable.
Polymers with polyisocyanurate structure are known for their high temperature stability and flame retardancy. Polyisocyanurate foams based on the aromatic diphenylmethane 4,4′-diisocyanate (MDI), for example, are in widespread use, especially as high-performance insulating materials, due to their very low thermal conductivity.
As a result, it would be desirable to provide improved methods of treating a wellbore within an underground formation using a treatment composition that overcomes at least some of the foregoing problems. Creating an effective polymeric plug or cement that can prevent the loss by solidifying in the loss zone at various down-hole temperatures is a need in the art. Especially challenging is creating a stable plug at down-hole temperatures of between 250° F. (121° C.) and 300° F. (149° C.).